One goal of the proposed project is to determine the role of the cytoplasmic triiodothyronine binding protein in tadpole metamorphosis. The liver and tail fin cytoplasmic triiodothyronine binding protein will be purified. Antibodies against the purified cytoplasmic triiodothyronine binding proteins will be developed in rabbits. These antisera will be used to determine the immunological similarity between the liver and tail fin cytoplasmic triiodothyronine binding proteins. The antisera will also be used to determine the content and immunological similarity of the triiodothyronine binding proteins in other tissues of the tadpole. A second part of this proposal concerns the investigation of the role of glucocorticoids in tadpole metamorphosis. The plasma concentration of corticosterone throughout natural and thyroid hormone induced metamorphosis will be determined by radioimmunoassay. The effect of glucocorticoids on various thyroid hormone induced morphological and biochemical changes will also be determined. Studies on the nuclear binding of thyroid hormones will be continued. The major aim is to determine the proper set of conditions under which saturation of the nuclear thyroid hormone binding sites can be achieved. Lastly, the binding of prolactin to a tissue known to be responsive to the hormone, the tail fin, will be compared to the binding in a tissue which does not respond, the liver. The change in association constant and number of binding sites will be assessed during natural and thyroid hormone induced metamorphosis and following prolactin treatment.